Parasitic infections continue to be an important problem in animal production. Prophylactic or therapeutic use of anthelmintic drugs is a standard practice for every farm, where pigs or all kinds of poultry species are reared. The requirements for an anthelmintic product that is suitable for use in the intensive pig and poultry industry are: a broad spectrum activity (active against all important worm species that can occur in pigs), potent activity against the adult as well as the larval stages of the worms and the products should also have a wide safety margin.
For pig production 3 main groups of products are used:                imidathiazoles (levamisole).        avermectins (ivermectin, doramectin,        benzimidazoles (flubendazole, fenbendazole, mebendazole, oxfendazole, albendazole, cambendazole, parbendazole, oxibendazole and cyclobendazole), and pro-benzimidazoles (febantel, thipophanate and netobimin).        
For the poultry industry the avermectins are excluded because of specific toxicity reasons and the choice is therefore largely limited to levamisole and a few benzimidazole compounds.
The administration of benzimidazole compounds to pigs and poultry has so far been limited to oral administration as a top dressing on the feed or admixed into the feed. Benzimidazoles are insoluble in water and therefore their administration via the drinking water has been virtually impossible.
Medication via drinking water is routinely used for prophylaxis and treatment of infectious diseases of intensively reared animals. The increased flexibility offered by medicating via water as compared to either parenteral or in-feed medication makes it an attractive alternative.
With drinking water treatment the major drawbacks of in-feed medication can be avoided:                medicated feed may not be immediately available when animals are sick        poor homogeneity of mix        segregation from feed during transport        variable individual intake        requires bulk storage        cross contamination (carry-over) of feed batches at the feed mill        difficult to manage withdrawal times        no flexibility in treatment and dosage schedules        sick animals stop eating and therefore stop taking the necessary mounts of medication.        
The effectiveness of medication via the drinking water largely depends on the quality of the formulation and the palatability of the medication. Such formulation should provide:                maximum availability of the drug        minimal segregation of the active compound in the water delivery systems, medication pumps, nipples, cups . . . etc.        a very precise dosing and homogeneous distribution in the water        a guaranteed stability of the active compound, irrespective of the quality of the water used.        
Many pig and poultry farms are already equipped with the necessary devices to administer the medication via drinking water. Such water delivery systems on farms are complex systems of tanks, pipes, coils, pen drinkers and nipples. An average stable may contain several hundreds of meters of pipes with many coils and hundreds of individual cups and/or nipples. The water in the watering system in a pig or poultry house obeys the principles of laminar flow through the pipes and coils and is subjected to the so called “shearing” forces which will affect the rate of flow. In such complex piping system there are considerable risks for segregation or sedimentation of the medication, certainly when it concerns water insoluble compounds.
The quality of the drinking water will vary considerably from region to region, some farmers even might use their own water supplies. This can have a very significant impact on the solubility or dispersibility of the medication into the drinking water.
Some products currently used in the drinking water (e.g. oxytetracycline) are not very readily soluble and solubility enhancing agents such as citric acid are often used to increase the solubility. It is known however that the use of citrate-based compounds may dislodge sediment and result in blocked nipples or drinkers. Low solubility with amoxicillin for example can result in a homogenous lump of powder floating unused in the main header tank or leading to blockage of water proportioners (L. Reeve-Lolinson, The Pig Journal 1998, 42, 74-86).
Research work has demonstrated that for the administration of benzimidazole compounds via the drinking water a very robust carrier system has to be used. The invention described hereafter demonstrates that a “Solid in Oil in Water” emulsion with specifically selected excipients provides an excellent carrier for the presented problem.
Normally, water insoluble veterinary drugs are administered in dry form through one of the following routes:                mixed into a dry feed blend, pelletised or not, and subsequently fed to the target animals of interest as a medicated feed        mixed with a special ingredient composition which may be pelletised or not as a medicated premix. This premix is dosed by the farmer on top of the normal feed supplied to the animals.        
These routes for medication are becoming less popular, due to the possibility of contamination of other feed blends with the active compound in the blending and transport equipment at the production facility, usually a feed mill. Another problem related to these routes of medication is the difficulty for the end-user, normally the farmer, to control the dosage of active compound per animal. In case of medicated feeds in mash form or medicated premixes in powder form the farmer can also be exposed to the active compound, which may pose health risks.
In case of liquid dosage of water-insoluble veterinary drugs, only trivial formulations for batch wise liquid dosage are described, with a limited stability. These formulations are not suitable for a reliable and reproducible dosage in a water distribution system. The problem is the impossibility to add these insoluble active compounds directly into the drinking water supply system, without occurrence of precipitation or creaming of the active compound in the storage vessel or in the water pipes during practical time scales of 3 up to 12 hours normally used in drug administration through drinking water systems. Up to the present no convenient solution was available for this route of medication of farm animals for water insoluble veterinary drugs.